Detailed chemical kinetic oxidation mechanism for a biodiesel surrogate

A detailed chemical kinetic mechanism has been developed and used to study the oxidation of methyl decanoate, a surrogate for biodiesel fuels. This model has been built by following the rules established by Curran et al. for the oxidation of n-heptane and it includes all the reactions known to be pertinent to both low and high temperatures. Computed results have been compared with methyl decanoate experiments in an engine and oxidation of rapeseed oil methyl esters in a jet stirred reactor. An important feature of this mechanism is its ability to reproduce the early formation of carbon dioxide that is unique to biofuels and due to the presence of the ester group in the reactant. The model also predicts ignition delay times and OH profiles very close to observed values in shock tube experiments fueled by n-decane. These model capabilities indicate that large n-alkanes can be good surrogates for large methyl esters and biodiesel fuels to predict overall reactivity, but some kinetic details, including early CO2 production from biodiesel fuels, can be predicted only by a detailed kinetic mechanism for a true methyl ester fuel. The present methyl decanoate mechanism provides a realistic kinetic tool for simulation of biodiesel fuels

Low- and intermediate-temperature ammonia/hydrogen oxidation in a flow reactor: Experiments and a wide-range kinetic modeling

Understanding the chemistry behind the oxidation of ammonia/hydrogen mixtures is crucial for ensuring the flexible use of such mixtures in several applications, related to propulsion systems and power generation. In this work, the oxidation of ammonia/hydrogen blends was investigated through an experimental and kinetic-modeling study, where the low- and intermediate-temperature conditions were considered. An experimental campaign was performed in a flow reactor, at stoichiometric conditions and near-atmospheric pressure (126.7 kPa). The mole fraction of fuels, oxidizer and final products was measured. At the same time, a comprehensive kinetic model was set up, following a modular and hierarchical approach, and implementing the recently-available elementary rates. Such a model was used to interpret the experimental results, and to extend the analysis to literature data, covering several oxidation features. The reactivity boost provided by H2 addition was found to be approximately linear with its mole fraction in both flow- and jet-stirred-reactor conditions (except for the smallest H2 amounts in the flow reactor), in contrast with the more-than-linear increase in the laminar flame speed. The key role of HO2 in regulating fuel conversion and autoignition at low temperature was confirmed for binary mixtures, with H2NO being the bottleneck to the low-temperature oxidation of NH3-rich blends. On the other hand, the nitrogen fate was found to be mostly regulated by NHx + NO propagation and termination channels

A Detailed Chemical Kinetic Reaction Mechanism for n-Alkane Hydrocarbons from n-Octane to n-Hexadecane

Detailed chemical kinetic reaction mechanisms have been developed to describe the pyrolysis and oxidation of the n-alkanes, including n-octane (n-C{sub 8}H{sub 18}), n-nonane (n-C{sub 9}H{sub 20}), n-decane (n-C{sub 10}H{sub 22}), n-undecane (n-C{sub 11}H{sub 24}), n-dodecane (n-C{sub 12}H{sub 26}), n-tridecane (n-C{sub 13}H{sub 28}), n-tetradecane (n-C{sub 14}H{sub 30}), n-pentadecane (n-C{sub 15}H{sub 32}), and n-hexadecane (n-C{sub 16}H{sub 34}). These mechanisms include both high temperature and low temperature reaction pathways. The mechanisms are based on previous mechanisms for n-heptane, using the same reaction class mechanism construction developed initially for n-heptane. Individual reaction class rules are as simple as possible in order to focus on the parallelism between all of the n-alkane fuels included in the mechanisms, and there is an intent to develop these mechanisms further in the future to incorporate greater levels of accuracy and predictive capability. Several of these areas for improvement are identified and explained in detail. These mechanisms are validated through comparisons between computed and experimental data from as many different sources as possible. In addition, numerical experiments are carried out to examine features of n-alkane combustion in which the detailed mechanisms can be used to compare processes in all of the n-alkane fuels. The mechanisms for all of these n-alkanes are presented as a single detailed mechanism, which can be edited to produce efficient mechanisms for any of the n-alkanes included, and the entire mechanism, with supporting thermochemical and transport data, together with an explanatory glossary explaining notations and structural details, will be available on our web page when the paper is accepted for publication

Oscillatory Behavior in Methane Combustion: Influence of the Operating Parameters

The influence of the main process parameters on the oscillatory behavior of methane oxidation was analyzed in conditions relevant for low-temperature combustion processes. The investigation was performed by means of direct comparisons between experimental measurements realized in two jet-stirred flow reactors used at atmospheric pressure. With the operating conditions of the two systems coupled, wide ranges of the inlet temperature (790-1225 K), equivalence ratio (0.5 < Φ < 1.5), methane mole fraction (XCH4 from 0.01 to 0.05), bath gases (i.e., He, N2, CO2, or H2O) and different overall mixture dilution levels were exploited in relation to the identification of oscillatory regimes. Although the reference systems mainly differ in thermal conditions (i.e., heat exchange to the surroundings), temperature measurements suggested that the oscillatory phenomena occurred when the system working temperature accessed a well-identifiable temperature range. Experimental results were simulated by means of a detailed kinetic scheme and commercial codes developed for complex chemistry processes. Simulations were also extended considering systems with different heat losses to the surroundings, thus passing from adiabatic to isothermal systems. Results highlighted the kinetic nature of the dynamic behavior. Because predictions were consistent with experimental tests, further numerical analyses were realized to identify the kinetics responsible for the establishment of oscillatory phenomena. Temperature oscillations were predicted for a significant reactor working temperature range, where oxidation and recombination kinetic routes, involving carbon C1-2 species as well as reactions of the H2/O2 sub-scheme, become competitive, thus boosting limit cycle behaviors. Oscillatory phenomena cease when the system working temperatures exceed characteristic threshold values with the promotion of faster oxidation routes that diminish the inhibiting effects of recombination reactions

The sensitizing effects of NO2and NO on methane low temperature oxidation in a jet stirred reactor

The oxidation of neat methane (CH4) and CH4doped with NO2or NO in argon has been investigated in a jet-stirred reactor at 107 kPa, temperatures between 650 and 1200 K, with a fixed residence time of 1.5 s, and for different equivalence ratios (Φ), ranging from fuel-lean to fuel-rich conditions. Four different diagnostics have been used: gas chromatography (GC), chemiluminescence NOxanalyzer, continuous wave cavity ring-down spectroscopy (cw-CRDS) and Fourier transform infrared spectroscopy (FTIR). In the case of the oxidation of neat methane, the onset temperature for CH4oxidation was above 1025 K, while it is shifted to 825 K with the addition of NO2or NO, independently of equivalence ratio, indicating that the addition of NO2or NO highly promotes CH4oxidation. The consumption rate of CH4exhibits a similar trend with the presence of both NO2and NO. The amount of produced HCN has been quantified and a search for HONO and CH3NO2species has been attempted. A detailed kinetic mechanism, derived from POLIMI kinetic framework, has been used to interpret the experimental data with a good agreement between experimental data and model predictions. Reaction rate and sensitivity analysis have been conducted to illustrate the kinetic regimes. The fact that the addition of NO or NO2seems to have similar effects on promoting CH4oxidation can be explained by the fact that both species are involved in a reaction cycle interchanging them and whose result is 2CH3+ O2= 2CH2O + 2H. Additionally, the direct participation of NO2in the NO2+ CH2O = HONO + HCO reaction has a notable accelerating effect on methane oxidation

A decadal view of biodiversity informatics: challenges and priorities

Biodiversity informatics plays a central enabling role in the research community's efforts to address scientific conservation and sustainability issues. Great strides have been made in the past decade establishing a framework for sharing data, where taxonomy and systematics has been perceived as the most prominent discipline involved. To some extent this is inevitable, given the use of species names as the pivot around which information is organised. To address the urgent questions around conservation, land-use, environmental change, sustainability, food security and ecosystem services that are facing Governments worldwide, we need to understand how the ecosystem works. So, we need a systems approach to understanding biodiversity that moves significantly beyond taxonomy and species observations. Such an approach needs to look at the whole system to address species interactions, both with their environment and with other species. It is clear that some barriers to progress are sociological, basically persuading people to use the technological solutions that are already available. This is best addressed by developing more effective systems that deliver immediate benefit to the user, hiding the majority of the technology behind simple user interfaces. An infrastructure should be a space in which activities take place and, as such, should be effectively invisible. This community consultation paper positions the role of biodiversity informatics, for the next decade, presenting the actions needed to link the various biodiversity infrastructures invisibly and to facilitate understanding that can support both business and policy-makers. The community considers the goal in biodiversity informatics to be full integration of the biodiversity research community, including citizens’ science, through a commonly-shared, sustainable e-infrastructure across all sub-disciplines that reliably serves science and society alike

Ammonia-methane interaction in jet-stirred and flow reactors: An experimental and kinetic modeling study

The influence of the addition of ammonia on the oxidation of methane was investigated both experimentally and numerically. Experiments were carried out at atmospheric pressure, using a fused silica jet-stirred reactor, and a recrystallized alumina tubular reactor designed on purpose to reach temperatures as high as ~2000 K. A temperature range of 600-1200 K was investigated in the jet-stirred reactor at a residence time of 1.5 s, while experiments in the flow reactor were carried out between 1200 and 2000 K, for a fixed residence time of about 25 ms in the reactive zone. A methane/ammonia mixture, diluted in helium, was used in both reactors with equivalence ratios varied between 0.5 and 2 in the first reactor, while stoichiometric conditions were investigated in the second one. The measurements indicate that CH4 reactivity was promoted by NH3 addition below 1200 K, but not so much influenced above. These results were interpreted and explained using a comprehensive kinetic model, previously validated over a wider range of operating conditions. The mechanism allowed to shed light on the underlying causes of the anticipated methane reactivity at low temperature, and of the major role played by NOx in it. This effect was shown to become less significant at higher temperatures, where the reactivity is mainly governed by H-abstractions on both fuels